In many adaptive optical systems, such as applications including laser pointing, tracking, welding, cutting, and melting, and laser communications and surveillance, among others, the direction, focal pattern, and other optical characteristics of directed, outgoing, high-energy laser light is controlled in response to incoming, return optical energy reflected from a targeted object. Attenuation, blooming, turbulence, and other phenomena induced by the propagation medium, however, distort and otherwise disturb both the outgoing and the return beams. To overcome the effects of such medium-induced phenomenon and point at a moving target, it is desirable to direct the outgoing optical energy toward the targeted object, and to receive the incoming return optical energy back therefrom, along a common, reciprocal, optical path. the outgoing optical energy and the return optical energy thereby undergo substantially self-cancelling medium-induced propagation distortions.
Coccoli, U.S. Pat. No. 4,281,896, incorporated herein by reference, provides a laser separator in which outgoing and return optical energy are separated along such a reciprocal optical path by an array of selectively inclined and spaced-apart planar mirrors. However, diffraction effects along its narrow dimension in many instances result in less than desirable levels of on-target optical energy and beam distortion, among other things.
It is also known to provide a laser separator in which the outgoing and the return optical energy are separated along a reciprocal optical path by a grating that is buried below the reflecting surface of a wavelength-selective mirror. The mirror is reflective at the wavelength of the outgoing optical energy, and it is transmissive to the return optical energy at another, different wavelength. The grating is responsive to the wavelength of the return optical energy and reflects it off at a predetermined angle, other than that predicated by Snells' law, onto a sensor. However, this type of reciprocal path laser separator not only tends to melt and otherwise disintegrate with high energy levels, but also its optical performance tends to significantly degrade with the presence of dirt, dust, and other such contaminants on the surface of the wavelength-selective mirror. In addition, the different wavelengths for the outgoing and the return optical signals require the provision of comparatively costly and complex electronic detection circuitry.